Method and system for steering a vehicle

ABSTRACT

This specification discloses a system for steering a wheeled vehicle characterized by employing, in addition to two steerable wheels attached to the vehicle frame, steering means for separately steering each steerable wheel within a portion of a circle in response to a steer signal; two sensing-comparators, each connected with one of the wheel steering means and operable to generate a steer signal in response to a primary control signal or a follower response signal and to discontinue the steer signal when the associated wheel has been steered through the number of degrees equivalent to the respective signal; actuator means for starting a turn by generating a turn signal; selector means connected with the actuator means and operable, in response to the turn signal, to select one of the wheels as a primary steerable wheel and to impart to the associated controller means the turn signal; controller means connected with the selector means and operable to impart to the sensing-comparator means associated with the primary steerable wheel and to a programmerfollower a primary control signal that is a function of the turn signal; a programmer-follower connected with the controller means and operable to generate and impart to the sensing-comparator means on a secondary steerable wheel; that is, the other of the two steerable wheels; a follower response signal related to the primary control signal as the number of degrees of rotation of a first focal point of a driven ellipse is related to a number of degrees of rotation of the opposite focal point of a driving ellipse rotating twice the number of degrees the primary steerable wheel is steered; the ellipse being identical, being tangential such that their focal points on their major axes form the four apices of a rectangle at the position equivalent to 0* of steer, having a first set of two of the focal points opposite, disposed a fixed distance apart and located at points fixed in space, and having the other two of the focal points opposite and in fixed spaced relation but free to move in space. The specification also describes a method of steering a vehicle, employing the unique follower response signal output from the programmer.

United States Patent [72] Inventor Ted L. Le Tournean Longview, Tex.[2]] Appl. No. 31,858 [22] Filed May 1,1970 [45] Patented June 22, 197i[731 Assignee R. G. Le Tournean, Inc.

Longview, Tex. Continuation of application Ser. No. 768,998, Oct. 21,1968, now abandoned.

[54] METHOD AND SYSTEM FOR STEERING A VEHICLE 33 Claims, ll DrawingFigs. [52] US. Cl l80/79.1, 244/77 [51] lot. Cl 862d 5/04 [56]References Cited UNITED STATES PATENTS 2,248,25l 7/l94l Reeves ISO/79.13,280,931 10/1966 Cahill et al ISO/79.1 X

Primary Examiner-A. Harry Levy Attorney-Wofiord and Felsham portion of acircle in response to a steer signal; two sensingcomparators, eachconnected with one of the wheel steering means and operable to generatea'steer signal in response to a primary control signal or a followerresponse signal and to discontinue the steer signal when the associatedwheel has been steered through the number of degrees equivalent to therespective signal; actuator means for starting a turn by generating aturn signal; selector means connected with the actuator means andoperable, in response to the turn signal, to select one of the wheels asa primary steerable wheel and to impart to the associated controllermeans the turn signal; controller means connected with the selectormeans and operable to impart to the sensing-comparator means associatedwith the primary steerable wheel and to a programmer-follower a primarycontrol signal that is a function of the turn signal; aprogrammer-follower connected with the controller means and operable togenerate and impart to the sensing-comparator means on a secondarysteerable wheel; that is, the other of the two steerable wheels; afollower response signal related to the primary control signal as thenumber of degrees of rotation of a first focal point of a driven ellipseis related to a number of degrees of rotation of the opposite focalpoint of a driving ellipse rotating twice the number of degrees theprimary steerable wheel is steered; the ellipse being identical, beingtangential such that their focal points on their major axes form thefour apices of a rectangle at the position equivalent to 0 of steer,having a first set of two of the focal points opposite, disposed a fixeddistance apart and located at points fixed in space, and having theother two of the focal points opposite and in fixed spaced relation butfree to move in space.

The specification also describes a method of steering a vehicle,employing the unique follower response signal output from theprogrammer.

AcTuAToR SELECTOR 4 LEFT RIGHT {CONTROLLER' PROGRAMMER CONTROLLER IRIGHT LEFT L FOLLOWER FOLLOWER LEFT RIGHT COMPARATOR COMPARATOR a? as 97 LEFT .i LEFT RIGHT RIGHT SENSING sT ERING STEERING SENSING MEANS MEANsMEANS MEANS PATENIED JUN22|971 SHEET 2 [IF 4 ACTUATOR W45 sELEcToR ,45

' I I O Q U Q I II #EFT RIGHT .CON ROLLER- GRAMM R co TRoLLER- RIGHT PROE A 59 LEFT FOLLOWER FOLLOWERE LEFT RGHT COMPARATOR COMPARATOR 67 a 7/ x145 9 1 LEFT L LEFT RIGHT RIGHT SENSING STEERING STEERING SENSING MEANsMEANs MEANS MEANs ,IINVENTOR.

wm /wmw ATTORNEYS PATENTEU M2219?! 3,586,117

' SHEET u or 4 A TTORNEYS METHOD AND SYSTEM FOR STEERING A VEHICLE Thisapplication is a continuation of my application, Ser. No.- 768,998,filed Oct. 21, 1968, and which has since become abandoned.

BACKGROUND 1. Field of the Invention The invention relates to a systemfor steering a wheeled vehicle. More particularly it relates to a systemeffecting differential steering to widely separated, individuallysteerable wheels.

2. Description of the Prior Art I The prior art has recognized that inorder to obtain perfect steering without drag or slippage on one of thesteerable wheels, it is essential that different degrees of steer beimparted to the inside wheel on the turn as compared with the outsidewheel on a turn.

The conventional method of achieving the different degrees of steerthatmust be imparted to the inner and the outer steerable wheels is by meansof a mechanical tiebar and drag link assembly oriented in the correctposition to compensate for this difference in steer. While the tiebarand drag link assembly are employed in conventional vehicles, they arenot suitable for many large load-carrying vehicles having widely spaced,individually steerable wheels; and particularly, are not applicable tothose carrying underslung loads such as the mobile type Gantry cranes.Since the space between the wheels must be free and clear of anyobstruction to handle cargo therein, the tiebar and drag link assemblycannot be employed without use of large and rigid mechanical leversbeing brought up the legs of the Gantry crane. Moreover in such heavyvehicles the force attending imperfect steerage is often great enough tocause structural damage, instead of merely dragging the tires on thepavement.

The prior art solutions attempting to solve the problem have employedhydraulic cylinder movement in conjunction with multiple and complexlinkage arrangements to effect differential hydraulic fluid flow to oneof the steerable wheels as compared with the other. Other attempts tosolve the problem have invoked the use of four wheel steering, eachwheel individually steerable through 360 of rotation and requiringelaborate means for maintaining the proper interrelationship between thefour wheels. None of the prior art solutions have been satisfactory inproviding a simple, economical method or system for effecting a nearlyperfect turn by a large vehicle having widely spaced, individuallysteerable wheels.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aportion of a wheeled vehicle advantageously employing the invention.

FIG. 2 is a design illustration schematically showing the location andmaximum degrees of steer of separately steerable wheels to effect a turnabout the midpoint of a line connecting two nonsteerable wheels of avehicle.

FIGS. 3a, 3b, and 3c are diagrams of tangential ellipses illustratingthe principlesemployed in the invention.

FIG. 4 is a block diagram illustrating schematically one embodiment ofthe invention.

FIG. 5 is a perspective view, partially schematic, of a portion of thesystem employed in the embodiment of FIG. 4.

FIG. 6 is a cross-sectional view of a portion of the system illustratedin FIG. 5.

FIGS. 7, 8 and 9 are pictorial views selected to illustrateschematically the interrelationships of significant parts of the systememployed in one embodiment of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS Applicant has discovered that aunique ellipsoidal program will describe the degrees of steer requiredto be imparted to two steerable wheels on a wheeled vehicle to verynearly effect a perfect turn. The unique ellipsoidal program operates onthe principle that identical ellipses, designed for the vehicle inaccordance with particulars described hereinafter, placed tangentialsuch that their focal points on their major axes form the four apices ofa rectangle, having a first set of opposite focal points disposed afixed distance apart and located at points fixed in space, and having asecond set of opposite focal points maintained in fixed spacedrelationship but movable in a plane to effect a number of degrees ofrotation of the driven ellipse which is twice the number of degrees ofsteer required to be imparted to a secondary steerable wheel when thedriving ellipse is rotated twice the number of degrees of steer to beimparted to a primary steerable wheel. Therefore, Applicant employs in asteering system a unique ellipsoidal programmer which operates upon' aprimary control signal employed to steer a primary steerable wheel toeffect a follower response signal to steer a secondary steerable wheel;that is, the other of the two steerable wheels; by carrying out theunique ellipsoidal program.

Thus, in accordance with the invention, a wheeled vehicle having twoseparately steerable wheels, each having a sensingcomparator inassociation therewith is steered by the method consisting essentially ofthe steps of:

a. generating a turn signal to effect a turn;

b. selecting one of the wheelsand the sensing-comparator associatedtherewith to be a primary wheel and a primary sensing-comparator for theduration of the turn;

c. generating and imparting to the primary sensing-comparator a primarycontrol signal that is a function of the turn signal;

d. sensing the primary control signal and in response thereto generatingin accordance with the unique ellipsoidal program and imparting to theother of the sensing-comparators a follower response signal; that is, asignal which is related to the primary control signal as the number ofdegrees of rotation of a first focal point of a driven ellipse isrelated to a number of degrees of rotation of the opposite first focalpoint of a driving ellipse rotating twice the number of degrees that theprimary wheel is steered; the ellipses being identical, being placedtangential such that their focal points on their major axes form theapices of a rectangle at the position equivalent to zero degrees ofsteer, having a set of first and opposite focal points disposed a fixeddistance apart and located at points fixed in space, and having theirother, respective, and opposite focal points on their major axes infixed spaced relationship but free to move in a plane;

e. steering the primary steerable wheel through a number of degrees thatis a function of the primary control signal; and

. steering the other steerable wheel through a number of degrees that isthe function of the follower response signal.

In accordance with another embodiment of the invention, there isprovided a steering system for use in a wheeled vehicle comprising:

a. a vehicle frame; I

b. two wheels attached to the frame and separately steerable, either ofwhich may be a primary steerable wheel or a secondary steerable wheel;

c. two steering means each connected, respectively, with one of thewheels and operable to steer that wheel within a portion of a circle inresponse to a steer signal;

d. two sensing-comparators each connected, respectively, with one of thewheels and with one of the steering means and operable to generate asteer signal in response to a primary control signal or a followerresponse signal and operable to discontinue the steer signal when thewheel has been steered through the number of degrees that is a functionof, respectively, the primary control signal'or a follower responsesignal;

e. actuator means for actuating a turn by generating a turn signal;

f. selector means connected with the actuator means and operable, inresponse to the turn signal, to select one of the wheels as a primarysteerable wheel for the turn and to impart to the controller means theturn signal,

g. controller means frame; with the selector means and operable toimpart to the sensing-comparator means associated with the primarysteerable wheel and to a programmer-follower a primary control signalthat is a function of the turn signal;

h. a programmer-follower connected with.the controller means andoperable to generate and impart to the sensing-comparator means on thesecondary steerable wheel a follower response signal inaccordance withthe unique ellipsoidal program.

In operation, the invention is employed in turning a vehicle such asillustrated in FIG. 1. Therein, wheels 11 and 13 are individuallysteerable whereas wheels 15 and 17 are not. The wheels are maintainedwidely separated by frame 19 providing space and handling apparatusbetween the wheels to facilitate handling of cargo, the specific cargohandling apparatus not being shown since it is well known and does notform a part of this invention. Each of the steerable wheels 11 and 13has a steering means such as steering motor 21 engaging a steering gear22 and operable to effect a desired degree of steer within a portion ofa circle. Similarly, each of the steerable wheels has a position sensor23 and a selsyn transmitter 25 for, respectively, sensing the degrees ofsteer imparted to the wheel and transmitting to a selsyn receiverasignal which is unique for each position of the wheel. I

With a vehicle such as illustrated in FIG. 1, the shortest turningradius is effected if the vehicle rotates about the midpoint of animaginary line drawn between the nonsteerable wheels. Thus, employing adesign scale model similar to the one illustrated in FIG. 2, the maximumangle a through which the outside wheel will be required to steer andthe maximum angle B through which the inside wheel will be required tosteer can be determined. As used herein, maximum angles refer toselected maximum angles to effect a turn about a particular point; suchas, the midpoint of a line between nonsteering wheels. Specifically, fora vehicle feet long and 27% feet wide the angle a will be 55 and theangle [3, which is a supplement of a, is 125. These maximum angles ofsteer are significant in designing the programmer, as discussedhereinafter. FIG. 2 shows that the wheels are normal to a line drawnfrom the midpoint of an imaginary line between the nonsteerable wheelsand therefore the vehicle will turn in a circle with the center of thecircle being the midpoint of the imaginary line between the nonsteeringwheels.

These maximum angles, a and B, determine the characteristics of theidentical tangential ellipses which form the basic principle upon whichthe invention is based. While the major axes for the identical ellipsesmay be arbitrarily chosen, the distance between the focal points on themajor axes is the length of the major axes multiplied by the cosine ofthe angle 0:. Similarly the length of the minor axes is the length ofthe major axes multiplied by the sine of 0.

FIGS. 30, 3b, and 3c illustrate the principle upon which Applicant'sinvention is based. Therein, identical ellipses 27 and 29 are placedtangential at point 31, such that the focal points on their major axesform the four apices of a rectangle at the position equivalent to 0 ofsteer of the steerable wheels of the vehicle illustrated in FIG. 1.Ellipses 27 and 29 are rotatable about their respective opposite focalpoints 33 and 35. Focal points 33 and 35 are disposed a fixed distanceapart and are fixed in space. Ellipses 27 and 29 have their other,respective, focal points 37 and 39 along their major axes maintained infixed spaced relationship as illustrated by dashed line 41 but free tomove in their plane of rotation.

When ellipse 27 is rotated about its focal point 33 through a number ofdegrees; for example 20 as shown in FIG. 3b; cl lipse 29 is rotatedabout its focal point 35 28 to retain tangential point of contact 31.Applicant has discovered that the relationship of thedegrees ofrotation; namely, 20 for ellipse 27 and 28 for ellipse 29; is the sameas, but twice as large in magnitude as, the degrees of steer that mustbe imparted respectively to the outer wheel and the inner wheel inmaking a turn having a large radius with a vehicle having the dimensionsillustrated in FIG. 2.

Similarly, as illustrated in FIG. 3c when ellipse 27 is rotated througha larger angle such as the 31, ellipse 29 is rotated through a muchlarger angle of 50 and these respective degrees of rotation are twicethe degrees of steer that must be imparted, respectively, to the outerwheel and the inner wheel when the vehicle is turned at a sharper rateof turn.

It is apparent from FIGS. 3:1 -30 that linkage equivalents can beemployed to replace the ellipses. For example, ellipse 27 can bereplaced by a rigid connection means, or rigid connection, between fixedfocal point 33 and the other focal point 39 on the major axis.Similarly, ellipse 29 can be replaced by a rigid connection betweenfixed focal point 35 and the other focal point 37 on the major axis. Alinkage is employed as illustrated by dashed line 41 to maintainconnecting means distance apart so as to retain the equivalent of atangential point between the ellipses.

In order for the relationship of the ellipses to continue to be the sameas for the inside and outside steerable wheels on the vehicle making theturn, the fixed focal points 33 and 35 must be opposite focal points andnot adjacent; that is, they must not be on the same side of the leverequivalent to dashed line 41. Yet it is apparent that, in extrapolatingthe trend illus trated in FIGS. 3a-3c, dashed line 41 will ultimatelyalign moveable focal points 37 and 39 with fixed focal point 35. Thisposition is referred to as dead center position. From this dead centerposition further turning of ellipse 27 could cause the lever equivalentto dashed line 41 to move back in the direction whence it came. In thisway fixed focal point 33 would be on the same side as fixed focal point35 and no longer be opposite focal points, in which case therelationship breaks down. It is imperative, therefore, that a means beprovided to move the ellipses, or their equivalents, from a dead centerposition such that the fixed focal points are maintained as oppositefocal points rather than adjacent focal points It is readily apparentthat if gear teeth are employed about the periphery of the ellipses, noproblem is encountered in this regard. Similarly, if gears are employedat the respective ends of the ellipses such that they mesh at the deadcenter position the problem is alleviated since rotation of one ellipseinsures counterrotation of the other. Applicant has found that it is notnecessary to use multiple gear teeth on the linkage equivalent of eachellipse, but that a single meshing means may be attached to the rigidconnections and located at the point equivalent to the maximumdimensions of the major axis of each respective ellipse and move therigid connections from the dead center position to maintain the fixedfocal points as opposite focal points; similarly, maintaining connectingmeans holding the lever equivalent to dashed line 41 as opposite focalpoints also.

One embodiment of the invention'is illustrated by the block diagram ofFIG. 4. Therein actuator means 43 is connected with selector means 45.Actuator means 43 is employed to initiate a turn of the vehicle andindicates whether a steer to the left or to the right is indicated.Signal is passed to the selector means 45 which discriminatesthe left orright signal to select which one of the steerable wheels 11 and 13 is tobe the primary steerable wheel for the duration of the particular turn.The other steerable wheel is thus relegated to a secondary steerablewheel. Selector means 45 is connected with two controller-followermeans, one being designated left controllerright follower 47 and theother being designated right controller-left follower 49. Thecontroller-follower means are each connected with programmer 51.Selector means 45 transmits the turn signal to the same controller asthe wheel selected as the primary steerable wheel. As illustrated by thesolid line from selector means 45 to left controller'right follower 47,the left steerable wheel has been selected as the primary steerablewheel and the turn signal transmitted to the left controller-rightfollower 47. Left controller-right follower 47 then transmits a primarycontrol signal that is a function of the turn signal to the leftcomparator 53 via signal conductor means 55 and to programmer 51 viainterconnection 57.

Programmer 51 operates on the primary control signal in accordance withthe unique ellipsoidal program and effects the proper follower responsesignal which it sends via second interconnection means 59 to rightcontroller-left follower 49. Right controller-left follower 49 transmitsthe' follower response signal via second signal conductor means 61 toright comparator 63.

Left comparator 53 is connected with left steering means 65 and leftsensing means 67 associated with left steerable wheel 13. Similarly,right comparator 63 is connected with right steering means 69 and rightsensing means 71 associated with right steerable wheel 11.

Thus, left comparator 53 sends a steer signal to left steering means 65via steer signal conductor 73. Simultaneously, right comparator 63 sendsa steer signal to right steering means 69 via second steer signalconductor 75. To afford feedback information, left sensing means 67senses the degrees of steer through which wheel 13 has been turned andsends this information back to left comparator 53 via feedback signalconductor 77.

Right sensing means 71 senses the degrees of steer through whichsteerable wheel 11 has been steered and sends this information back toright comparator 63 via second feedback signal conductor 79. Once wheel13 has been steered through the number of degrees that is functionallyequivalent to the primary control signal, left comparator 53 terminatesthe steer signal to left steering means 65. In like manner, once wheel11 has been steered through the number of degrees that is functionallyequivalent to the follower response signal, right comparator 63terminates the steer signal to the right steering means 69. Steerablewheels 11 and 13 retain the degrees of steer imparted thereto untilanother turn signal is initiated by actuator means 43. Selector means45, however, maintains the same wheel as the primary steerable wheeluntil the wheels are returned to 0 of steer, also referred to as neutralposition. Consequently, when actuator means 43 begins to finish the turnby actuation of a return to 0 of steer, selector means 45 continues tofeed the signal from the actuator means 43 to left controller-rightfollower 47. in response thereto, left controller-right follower 47sends a primary control signal indicating an opposite direction of steerto left comparator 53 and programmer 51. As before, programmer 51operates upon the primary control signal in accordance with the uniqueellipsoidal program and sends the proper follower response signal toright controller-left follower 49. Right controllerleft follower 49sends the follower response signal, indicating an opposite direction ofsteer to that originally sent, to right comparator 63 via second signalconducting means 61.

The sequence of operations in returning to 0 of steer, or any otherindicated position intermediate the original turn indication and 0 ofsteer is effected in the same way described hereinbefore with respect tothe original turn.

Once 0 of steer have been reached and a turn in the opposite directionis initiated by actuator means 43, selector 45 selects the oppositewheel as the primary steerable wheel. Consequently, as illustrated bythe dotted line, selector means 45 transmits the turn signal to rightcontroller-left follower 49. Thereafter the sequence of operations is,in principle, the same although the converse of those described withrespect to the original turn. Specifically, right controller-leftfollower 49 sends a primary control signal to right comparator 63 and toprogrammer 51. Programmer 51 operates upon the primary control signal inaccordance with the unique ellipsoidal program to effect and transmit tothe left controller-right follower 47 the proper follower responsesignal.

As described before, the respective comparators generate and transmitthe proper steer signals until the wheel is steered, and the sensingmeans feeds back the information that the wheel is steered through theproper number of degrees. The steer signals are then terminated. Furthersteering is carried out in accordance with one of the modes describedhereinbefore; namely, further steering in the same direction, a returnto neutral, or further steering from neutral position.

The vital operation of the unique ellipsoidal programmer in conjunctionwith the other elements of the invention can be clearly seen in F [68.59 illustrating in detail one embodiment of the invention. Referring toFIG. 5 actuator means 43 may comprise steer switch 81 having a togglebar 83 mounted on the operator's console and adapted to generate a leftsteer signal when moved in one direction and for generating a rightsteer signal when moved in another direction. Steer switch 81 isconnected with reversible electric motor 85 by electrical conductors 87and 89. Electric motor 85 is physically connected with drive gear 91 andoperable to rotate drive gear 91 while motor85 remains fixed. Drive gear91 engages idler gear 93 mounted adjacent thereto on idler shaft 95 andbushings 97, FIG. 6. Frame subunit 99 maintains the integrity of thesubassembly and affords mounting points for the various units as well asthe bushings for the various shafts. Atthe position equivalent to 0 ofsteer, drive gear 91 engages at least a single tooth of sector gear 101serving as one of the controller-follower means; and similarly idlergear 93 engages at least a single tooth of second sector gear 103serving as the other of the controller-follower means. I

First shaft 105 serves as a fixed focal point 33 for the equivalent ofellipse 27. Similarly, second shaft 107 serves as fixed focal point 35for the equivalent of ellipse 29. Shaft 105 is connected so as to rotatewith sector gear 101 and shaft 107 is connected so as to rotate withsector gear 103. Shaft 105 has a rigid connection means; such as lever109; with a first connecting means; such as pin 111; located at thepoint in space that is equivalent to the other focal point 39 on themajor axis of ellipse 27. Similarly shaft 107 has a rigid connectionmeans; such as second lever 113; with a second connecting means; such assecond pin 115; located at the point in space that is equivalent to theother focal point 37 on the major axis of the ellipse 29. Pins 111 and115 are connected by bar 117 and are maintained the same distance apartas levers 109 and 113 are rotated about their respective shafts 105 and107. While this linkage arrangement between levers, pins, and shafts issufficient to negotiate turns requiring low degrees of steer, it isimperative that meshing means be provided in the linkage arrangementsimulating the ellipses where large degrees of steer are to be impartedto one or more of the wheels, as described hereinbefore. Therefore,meshing means; such as tooth 119 and notch 121; are provided on theextension of lever 109 and located in space equivalent to the maximumdimensions of the major axis of the ellipse being simulated. Similarly,the converse meshing means are provided on lever 113 by notch 123 andtooth 125. In this way, the meshing means move the rigid connectionsfrom the dead center position and maintain the proper relationship ofthe linkages in which shafts 105 and 107 remain as simulating oppositefocal points. To engage properly, the meshing means have an equivalentradius that is equal to the equivalent ellipse major axis multiplied by(sina).

Shafts 127 and 129 serve as the respective signal conductor means fromthe controller-follower means. Attached to shafts 127 and 129 androtatable therewith are the respective comparators which comprise holder131 with two U-shaped ends, each having affixed thereto a light source133 and an electronic device 135 rendered conductive by the impingementof light thereupon. While the electronic device 135 may be any of thephotosensitive cells, it is preferred that it be a solid state devicewhich is rendered conductive when light from light source 133 impingesthereupon. Electronic device 135 is connected in a circuit with a sourceof power and with the steering means for one of the steerable gears. Thecircuit itself is not shown in order to simplify presentation and sincesuch circuits are well known. lnterposed between light source 133 andelectronic device 135 on the U-shaped ends of holder 131 is indicatorplate 137, comprising a circular plate having an opaque portion operableto interrupt impingement of light from light source 133 on electronicdevice 135, but having a cutaway portion which allows light to betransmitted from light source 133 to electronic device 135. Asindicated, to permit operability regardless of the direction of steer,holder 131 has two light sources and two electronic devices andindicator plate 137 extends through an entire 360 range. The cutawayportion extends through slightly less than 180, whereby the indicatorplate blocks the light from both electronic devices at equilibrium;i.e., when the respective wheels have the correct degrees of steer; buttransmits the light to one electronic device or the other to indicate aparticular direction of steer at nonequilibrium conditions; e.g., when awheel does not have the correct degrees of steer as when the holder isrotated.

Indicator plates 137 are mounted upon their respective shafts; such asshaft 139; and adapted to assume a slave posi tion in response to aslave selsyn receiver 141. The slave selsyn receivers, illustrated as141, are connected with selsyn transmitters; such as 25, FIG. 1; andadapted to assume a slave position for each unique signal from theselsyn transmitter. Selsyn transmitter 25 is connected with positionsensor 21 at a steerable wheel and adapted to transmit a unique signalfor each position indication of the position sensor. Indicator plate137, however, moves through twice the number of degrees of rotationequivalent to the number of degrees of steer of the particular steerablewheel to which it is ultimately enslaved. Together, indicator plate 137,selsyn transmitter 25 and selsyn receiver 141, position sensor 23, andthe interconnection means therebetween comprise sensing means 67,feedback signal conductor 77, and mechanical interconnection 143 betweenthe wheel 13 and left sensing means 67 in FIG. 4.

For additional clarity, FIGS. 7, 8, and 9 have been provided toillustrate the coaction between the elements and their respectivepositions for the embodiment and example described hereinbefore, duringpositions of, respectively, of steer, maximum degree of steer to theright, and maximum degrees of steer to the left.

In FIG, 7 showing the neutral position, drive gear 91 meshes with idlergear 93 and engages a single tooth of sector gear 101. Idler gear 93engages a single tooth of sector gear 103. In the unique ellipsoidalprogrammer 51, levers 109 and 113, representing the major axes of theirrespective ellipses are parallel at this position of 0 of steer of therespective steerable wheels 11 and 13, and shafts 105 and 107 and pins111 and 115 form the apices of a rectangle. In this position, the opaqueportion of indicator plates 137 block the light from light sources 133such that the electronic devices (not shown) are not conductive an nosteer signal is imparted to the wheels.

Referring to FIG. 8 and assuming that it is desired to turn the vehicleillustrated in FIG. 2 such that the vehicle rotates about the midpointof an imaginary line between the nonsteerable wheels, the steer switch81, FIG. 5, is activated to the right position. Reversible motor 85,FIG. 5, turns drive gear 91 which in turn rotates idler gear 93 in theopposite direction. In this example the selector means will choose theright steerable wheel 11 as the primary steerable wheel. Therefore,drive gear 91 rotates clockwise, engaging sector gear 101 and rotatingit in a counterclockwise direction.

Once sector gear 101 begins to rotate, holder 131 is also rotated suchthat light from the light source impinges upon the electronic deviceeffecting a steer right signal to the right wheel 11, which is theprimary steerable wheel for the duration of this turn and which must beturned to the maximum angle a of 125. Sector gear 101 is rotated throughtwice the number of degrees that wheel 11 will be required to steer.Expressed otherwise, sector gear 101 will rotate through 250.

As soon as drive gear 91 rotates sector gear 101, idler gear 93, turningin the opposite direction, disengages from sector gear 103 leaving itfree to respond to rotational signals from the programmer 51.

Simultaneously, shaft 105 effects rotation of lever 109. Bar 117transmits this rotational force from shaft 105, serving through itslinkage arrangement as the equivalent of ellipse 27, to impart rotationvia lever 113 to shaft 107. The rotation imparted to shaft 107 will beless, however, than the rotation of shaft 105. Sector gear 103, havingdisengaged from idler gear 93 is free to rotate in response to urgingoflever 113 and in turn rotates its holder efiecting a steer rightsignal since opaque portion of its indicator plate no longer blocksimpingement of light from the light source upon the electronic devicecarried in the holder and effecting a steer right signal. Consequently,from the holder, acting as a comparator, the steer right signal is sentto steering motor and wheel 13 is steered to the right.

The steer right signals continue to be sent to the respective gearsuntil they have been steered to the number of degrees indicated by thecomparator; that is, the position of the holders. In order to determinewhen this has been accomplished, feedback information is given from eachwheel by the position sensor whose position is transduced into a uniquesignal and transmitted by the selsyn transmitter to the slave selsynreceiver associated therewith. The slave selsyn receiver positions itsindicator plate to a position equivalent to the number of degrees ofsteer of the respective wheels. Thus, when the maximum number of degreesof steer has been accomplished as illustrated in FIG. 8, indicatorplates 137 for the respective holders again block, through their opaqueportion light from light sources 133 and render nonconductive electronicdevices 137. This terminates the steer signal. In FIG. 8 it can be seenthat sector gear 101 will have rotated counterclockwise through 250 butis still retained in engagement with drive gear 91 by one tooth, as itinitially engaged drive gear 91. Similarly, sector gear 103 which isoperated as a follower responding to rotational urging from programmer51 is rotated without the toothed portion of the sector gear engagingidler gear 93, but when the maximum degree of steer has been impartedone tooth again engages idler gear 93. In this way the selector retainsthe same wheel as the primary steerable wheel even though the actuator,or steer switch 81, may be moved to the left to start the turn to 0 ofsteer.

When the steer switch is moved to the left, the reversible electricmotor rotates in the opposite direction, rotating drive gear 91 in theopposite direction to its original direction. Thus, drive gear 91 isrotated counterclockwise, effecting clockwise rotation of sector gear101 and idler gear 93. The clockwise rotation of idler gear 93disengages from the tooth of sector gear 103, which is again free torotate in response to torque applied from programmer 51. The reverserotation of sector gear 101 moves its holder 131 in the oppositedirection, whereby the light source clears the opaque portion ofindicator plate 137 and activates the electronic device effecting asignal to steer in the opposite direction to the steering motor at wheel11.

In the reverse operation sector gear 103 is rotated through the missingportion, which happens to be or twice the angle a to which the outsidewheel is to be steered. Once the holder attached to shaft 129 of sectorgear 103 is rotated, the light source moves beyond the opaque portion ofits indicator plate and renders conductive its electronic device. Thiseffects a steer left signal to the steering motor which steers wheel 13back toward a neutral position.

FIG. 9 illustrates the converse of the situation of FIG. 8 in which themaximum degree of steer to the left is effected to turn the vehicleillustrated in FIG. 2 in a circle about the midpoint of the line betweenthe nonsteerable wheels. Again, steer switch 81 has its toggle moved tothe left position effecting rotation of reversible motor 85. Motor 85,in turn, effects rotation of drive gear 91, this time in acounterclockwise direction. Idler gear 93 engaged therewith is thusrotated in a clockwise direction as is sector gear 101. As shown howeversector gear 101 rotates through only one tooth before it disengagesleaving it free to respond to the rotational urging from programmer 51.Idler gear 93 rotates sector gear 103 counterclockwise. Once sector gear103 rotates, its holder is rotated and light from its light sourcerenders conductive its electronic device signaling a steer left to wheel13 which has been selected as the primary steerable wheel for a turn tothe left.

In this turn to the left, shaft 107 serves as the focal point for thedriving ellipse and rotates lever 113. The other focal point on themajor axis, designated pin 115 transmits the force via bar 117 to lever109, effecting rotation of shaft 105 and con-- sequently rotation ofsector gear 101. Once sector gear 101 is rotated holder 131 is rotated.Consequently, light from its light source moves off the opaque portionof indicator plate 137 and signals a steer left signal to wheel 11.

As previously described, the steer signal is continued until thesteering motor has turned the respective wheel one-half the number ofdegrees rotated by the holder. Once these number of degrees have beeneffected, as indicated by the position sensor, selsyn transmitter,selsyn receiver and indicator plate, the steer signal is terminated. Theextreme position of turn is indicated in FIG. 9 in which sector gear 103has turned through 250, effecting 125 of steer to wheel 13 which in turneffects slave rotation of the indicator plate through 250. Sector gear103 retains one tooth in engagement with idler gear 93.

Responsive to the rotational urging from programmer 51 sector gear 101has rotated through its free space of essentially l l, effecting 55 ofsteer to wheel 1 1. Sector gear 101, in its ultimate posltlon of extremeleft steer engages one tooth with drive gear 91.

As previously discussed with respect to the turn to the right, theselector means retains the same wheel as the primary steerable wheeleven though the steer switch may be moved to the right position toreturn the wheels to neutral. To do so, steer switch has its toggle 83moved to the right, actuating reversible electric motor 85 and rotatingdrive gear 91 clockwise. This effects counterclockwise rotation of idlergear 93 and disengagement of sector gear 101 with drive gear 91.Counterclockwise rotation of idler gear 93 effects clockwise rotation ofsector gear 103, generating a steer right signal to wheel 13 which hasbeen retained as the primary steerable wheel. in the manner indicatedhereinbefore, sector gear 101 is rotated in response to urging fromprogrammer 51 and generates a steer right signal, effecting a steer tothe right for wheel 11, the secondary steerable wheel. The steer signalscontinue in this way, until neutral position is again achieved.

in the event a continued turn is to be effected beyond neutral, thesteer signals will continue uninterrupted, even though the selector willselect a different steerable wheel to be the primary wheel for this newturn. As can be seen from FIG. 7, however, the sector gears meshsmoothly with either the drive gear or idler gear and the sequencedescribed hereinbefore begins without interruption of the steer signal.

While a turn of vehicle about a point; such as the midpoint of the linebetween its nonsteerable wheels; can be effected without difficultiesfrom unequal intervals of time required for the inside and outsidewheels to reach their maximum degree of steer, applicant has found itadvantageous to incorporate a speedup cam to increase the rate at whichthe degrees of steer are effected in the inside wheel when a vehicle ismaking a turn with some forward speed. it has been found advantageous toincorporate a cam which effects this higher rate of inducing steer tothe inside wheel when the steer range is between about one-fourth andthree-fourths a, a being the maximum degree of steer to be imparted tothe inside wheel. in the vehicle illustrated in FIG. 2, in which a is125", degrees, the cam is situated to effect an increased speed between31 and 93. When degrees of steer greater than 93 are to be imparted ithas been found advantageous to again return to a normal rate of steer toprevent overrun in the degrees of steer imparted because of the inertiaof the heavy armature of the steering motor.

The cams for introducing the greater rate of steer to the wheels areshown in FIGS. -9 as cams 145 and 147. Thus, when the sector gearrepresenting the primary steerable wheel has been turned through 62,equivalent to 31 of steer to be imparted to the primary steerable wheelin the examples, the

raised lobe on the particular cam will activate a microswitch to effectthe higher rate of steer. The respective microswitches are indicated as149 and 151. Thus, for example, in a turn to the right, once sector gear101 has rotated 62, cam 147 depresses microswitch 151 and causessteering motor to speed up and impart a greater rate of steer. It hasbeen found that the greater rate of steer is preferably about four timesthe normal rate of steer to minimize any forces acting on the wheels dueto the time delay in effecting the greater degree of steer to the insidewheel in a turn. The greater rate of steer is maintained by the cam 147until sector gear 101 has moved through 186 of steer, equivalent to 93ofsteer to be imparted to wheel 11.

in the reverse process, the lobe on cam 147 effects the greater rate ofsteer at 186 of rotation going back down, and maintains it until backdown to 62 of rotation of sector gear 101.

Conversely, in a turn to the left cam 145 depresses microswitch 149 atthe same degrees of rotation of sector gear 103; namely, 62 andmaintains the high rate of steer until 186 of rotation has beeneffected. in like manner in steering back to the neutral position cam145 effects the high rate of steer when 186 of rotation is reached andmaintains the high rate of steer until 62 of rotation is reached, whenagain the normal rate of steer is imparted.

it is noteworthy that the comparator provides a self-correctingmechanism. For example, should there be an oversteer because of theinertia of the steering motor, the oversteer would be reflected in theposition of the indicator plate which would, at the correct position,block light from the light source to the electronic device effecting thesteer signal and then would allow light from the other of the lightsources to impinge upon the other of the electronic devices, therebyeffecting a steer signal in the opposite direction to correct theoversteer. v

The embodiment .of the invention illustrated in FlGS. 7-9 has beendescribed with respect to selecting, as the primary steerable wheel, theinside wheel in a turn. in this instance, the primary steerable wheel issteered through a greater number of degrees than the secondary steerablewheel, which is the outside wheel of the turn. The method or apparatusof the invention is equally applicable when the outside wheel of a turnis selected as the primary steerable wheel. The same apparatus may beemployed as described hereinbefore. The only change required is that thesector gears are formed with the toothed section being approximatelyequal in angular dimensions to the blank sector illustrated. To be bemore exact, the blank sector has a dimension of 2a less one tooth forthe vehicle illustrated; that is, 1 10 minus the dimensions of onetooth. On the other hand, when the outside gear is selected as theprimary steerable gear, the toothed section of the sector gear will beplus one tooth whereas the blanked sector of the sector gear will occupy250, or 2B in the example illustrated, minus one tooth. it will beimmediately apparent that the driving ellipse, which is associated withthe primary steerable wheel, will turn through a lesser number ofdegrees when the outside wheel is the primary steerable wheel than doesthe driven ellipse associated with the secondary wheel, which would bethe inside wheel.

ONe of the advantages of the machine employing a simulation of theunique ellipsoidal programmer is that the rigid connection means, suchas lever 109 and bar 117 simulating dashed line 41 are the same length;i.e., the length of the major axis of the ellipse; and can be used forany vehicle. All that must be done is to locate the respective focalpoints such that the criteria described hereinbefore are satisfied.

The relationship of the angles a and B has been illustrated with respectto a simple, symmetrical vehicle with nonsteering wheels. The criteriaof design with respect to a and B are valid for any given point aboutwhich the vehicle is to be steered, regardless of the number ofsteerable wheels on the vehicle, and whether or not there arenonsteerable wheels on the vehicle.

it will be readily apparent that electrical, hydraulic or mechanicalsystems, servos and signals can be employed in any combination insteadof the specific elements described in detail herein Moreover while theinvention has been described with a high degree of particularity, it isunderstood that the present disclosure has been made only by wayofexample and that numerous changes in the details of construction andthe combination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What I claim'is:

, l. A method of steering a vehicle having two separately steerablewheels each having a sensing-comparator, consisting essentially of thesteps of:

a. generating a turn signal to effect a turn of the vehicle;

b. selecting one of said wheels and the sensing-comparator associatedtherewith to be a primary wheel and a primary sensing-comparator forsaid turn;

c. generating and imparting to said primary sensing-comparator a primarycontrol signal which is a function of said turn signal;

d. sensing said primary control signal and in response theretogenerating and imparting to the other of said sensing-comparators afollower response signal which is related to said primary control signalas the number of degrees of rotation of a first focal point of a drivenellipse is related to a number of degrees of rotation of the oppositefirst focal point of a driving ellipse rotating twice the number ofdegrees that the primary steerable wheel is steered; said ellipses beingidentical, being placed tangential such that their focal points on theirmajor axes form the apices of a rectangle at the position equivalent toof steer, having a set of first and opposite focal points disposed afixed distance apart and located at points fixed in space, and havingtheir other, respective, and opposite focal points on their major axesin fixed spaced relationship but free to move in a plane; steering saidprimary wheel through a number of degrees that is a second function ofsaid primary control signal; and

f. steering the other wheel through a number of degrees that is saidsecond function of said follower response signal.

2, The method of claim 1 wherein two outside nonsteering wheels are alsoattached to said frame and said identical ellipses have a distancebetween the two focal points on each respective major axis of eachellipse that is equal to said major axis multiplied by the cosine of anangle agenerated by lines extending from a midpoint between saidoutside, nonsteering wheels attached to said frame to one of saidoutside, nonsteering wheels and to the steerable wheel on the same sideas said one of said outside, nonsteering wheels and said ellipses haveeach respective minor axis length that is equal to said major axislength multiplied by the sine of the angle a.

3. The method of claim 2 wherein said primary wheel is the outside wheelon a turn and the driving ellipse rotates through a lesser number ofdegrees than said driven ellipse.

4. The method of claim 2 wherein said primary wheel is the inside wheelon a turn and said driving ellipse rotates through a greater number ofdegrees than said driven ellipse.

5. The method of claim 2 wherein said primary wheel is maintained as theprimary steerable wheel through steer in the opposite direction of saidturn until 0 of steer is again effected.

6. The method of claim 2 wherein a normal rate at which an inside wheelon a turn is steered is increased to a higher rate at an angle betweenabout one-fourth B and three-fourths B, where ,B is the maximum anglethe inside wheel would be required to be steered to effect a turn ofsaid vehicle about the midpoint of a line connecting its nonsteeringwheels.

7. Ihe method of claim 6 wherein said higher rate is four times as greatas said normal rate.

8. The method ofclaim I wherein said primary wheel is the outside wheelon a turn and the driving ellipse rotates through a lesser numberofdegrees than said driven ellipse.

9. The method of claim 1 wherein said primary wheel is the inside wheelon a turn and said driving ellipse rotates through a greater number ofdegrees than said driven ellipse.

10. The method of claim 1 wherein said primary wheel is maintained asthe primary steerable wheel through steer in the opposite direction ofsaid turn until 0 of steer is again effected.

11 The method of claim 1 wherein a normal rate at which an inside wheelon a turn is steered is increased to a higher rate at an angle betweenabout one-fourth B and three-fourths B, where B is the maximum angle theinside wheel would be required to be steered to effect a turn of saidvehicle about the midpoint ofa line connecting its nonsteering wheels.

12. The method of claim 11 wherein said higher rate is four times asgreat as said normal rate.

13. in a wheeled vehicle, a steering system comprising:

a. a vehicle frame;

b. two wheels attached to said frame and separately steerable, either ofwhich may be a primary steerable wheel or a secondary steerable wheel;

c. two wheel steering means, each connected, respectively, with one ofsaid wheels and operable to steer said wheel within a portion of acircle in response to a steer signal;

d. two sensing-comparators, each connected, respectively, with one ofsaid wheels and with the one of said wheel steering means associatedtherewith and operable to generate a steer signal in response to aprimary control signal or a follower response signal and operable todiscontinue said steer signal when said wheel has been steered throughthe number of degrees that is functionally equivalent to, respectively,said primary control signal or said follower response signal; actuatormeans for actuating a turn by generating a turn signal;

f. selector means connected with said actuator means and operable, inresponse to said turn signal, to select one of said wheels as a primarysteerable wheel for said turn and to impart to a controller means saidturn signal;

g. controller means connected with said selector means and operable toimpart to the sensing-comparator means associated with said p'rimarysteerable wheel and to a programmer-follower a primary control signalthat is a function of said turn signal;

h. a programmer-follower connected with said controller means andoperable to generate and impart to the sensing-comparator meansassociated with the secondary steerable wheel a follower response signalrelated to said primary control signal as the degrees of rotation of afirst focal point of a driven ellipse is related to the number ofdegrees of rotation of the opposite first focal point of driving ellipserotating twice the number of degrees that said primary steerable wheelis steered; said ellipses being identical, being placed tangential suchthat their focal points on their major axes form the apices of arectangle at the position equivalent to 0 of steer, having a set offirst and opposite focal points disposed a fixed distance apart andlocated at points fixed in space, and having their other, respective,and opposite focal points on their major axes in fixed spacedrelationship but free to move in a plane.

14. The steering system of claim 13 wherein said programmer employs asthe equivalent of said ellipses a first shaft simulating the focal pointof said driving ellipse and having rigid connection means with a firstconnecting means located at the point in space that is equivalent to theother focal point on the major axis of said driving ellipse, and asecond shaft simulating the opposite focal point of said driven ellipseand having second rigid connection means with a second connecting meanslocated at the point in space that is equivalent to the other focalpoint on the major axis of said driven ellipse; said first connectingmeans and said second connecting means being maintained in fixed spacedrelationship but free to move in a plane, and as opposite focal pointsby a connecting bar;

and meshing means attached to said rigid connection means and located atthe points in space equivalent to the maximum dimensions of the majoraxis of each respective ellipse to move said rigid connection means fromdead center position and maintain said shafts as opposite focal points.

15. The steering system of claim 14 wherein the distance between focalpoints of each respective ellipse and hence the distance between saidrespective shafts and connecting means is the major axis multiplied bythe cosine of an angle a generated by lines extended from a midpointbetween outside nonsteering wheels attached to said frame to one of thenonsteering wheels and to the steerable wheel on the same side as saidone of said nonsteering wheels, and the minor axis length is the majoraxis length multiplied by the sine of the angle a.

16. The steering system of claim 14 wherein the effective radius of saidrespective meshing means is equal to the ellipse major axis multipliedby (sine a).

17. The steering system of claim 13 wherein said wheel steering means isan electric motor turning an arrangement of gears connected so as toimpart steer to said wheel in response to rotation of said motor.

18. The steering system of claim 13 wherein said actuator consistsessentially of a turn switch mounted on an operator's console andadapted for generating a turn left signal when moved in one directionand for generating a turn right signal when moved in another direction;a reversible electric motor electrically connected with said turn switchand operable to rotate in either direction in response to the particularturn signal from said turn switch.

19. The steering system of claim 13 wherein said selector means consistsessentially of a drive gear and meshing therewith an idler gear; saiddrive gear connected with said reversible electric motor of saidactuator means and rotatably responsive to torque therefrom and operableto impart torque to one controller means duringturn in one direction,initiated from a position of of steer; and said idler gear maintained inengagement with said drive gear and rotatable about a fixed axis, andoperable to transmit torque from said drive gear to the other controllermeans during a turn in the opposite direction, initiated from 0 ofsteer.

20. In a wheeled vehicle, a steering system comprising:

a. a vehicle frame;

b. two wheels attached to said frame and separately steerable, either ofwhich may be a primary steerable wheel or a secondary steerable wheel;

c. two wheel steering means, each connected, respectively, with one ofsaid wheels and operable to steer said wheel within a portion of acircle in response to a steer signal;

d, two position sensing means, each connected, respectively, with one ofsaid wheels for sensing the number of degrees of steer of said wheel andfor generating and transmitting a signal that is a function of saiddegrees of steer;

e. two comparator means, each connected, respectively, with one ofsaidsteering means and connected with the one of said position sensingmeans associated with one of said steering means, and operable togenerate a steer signal in response to a primary control signal or afollower response signal and to terminate said steer signal when saidsensing means indicates said wheel has been steered through the numberof degrees that is functionally equivalent to, respectively, saidprimary control signal or said follower response signal;

f. two controller means, each connected, respectively, with one of saidcomparator means and operable to generate a primary control signal inresponse to a turn signal from an actuator or a follower response signalin response to a programmer;

g. selector means connected with said two controller means and operableto impart a turn signal singly and'respectively to said controllermeans;

h. actuator means connected with said selector means for generating aturn signal for actuating a turn;

i. a programmer connected with said two controller means and operable toreceive a primary control signal from either of said controller meansand in response thereto, to generate and transmit to the other of saidcontroller means a follower response signal, said programmer havingsignal translating means effecting a ratio of said follower responsesignal to said primary control signal that is the same as the ratio ofthe degrees of rotation of a first focal point of a driven ellipse tothe number of degrees of rotation of the opposite first focal point of adriving ellipse rotating twice the number of degrees that said primarysteerable wheel is steered; said ellipses being identical, being placedtangential such that their focal points on their major axes form theapices of a rectangle at the position equivalent to 0 of steer, having aset of first and opposite focal points disposed a fixed distance apartand located at points fixed in space, and having their other,respective, and opposite focal points on their major axes in fixedspaced relationship but free to move in a plane.

21. The steering system of claim 20 wherein said position sensingmeans'consists essentially of a position sensor sensing the degrees ofsteer of the respective wheel with which it is associated and generatinga unique signal which is a function of said degrees of steer, a selsyntransmitter generating and transmitting a signal unique to the positionindicated by said position sensor, a slave selsyn receiver connectedwith said selsyn transmitter and adapted to assume a slave position foreach unique signal therefrom, said slave position being relatable to thedegrees of steer of said wheel, and a slave pivotable indicator plateresponsively connected with said slave selsyn receiver and adapted toassume said slave position.

22. The steering system of claim 20 wherein said comparator meansconsists essentially of a holder having at each of its two U-shaped endsa light source and an electronic device rendered conductive by saidlight source, each electronic device being connected in a circuit with apower source and one of said wheel steering means and operable to send adirectional steer signal to said one of said wheel steering means whenbombarded by light from said light source.

23. The steering system of claim 20 wherein said controller means is asector gear rotatable about a fixed axis in response, respectively,tourging from said selector means or said programmer.

24. The steering system of claim 20 wherein said programmer employs asthe equivalent of said ellipses a first shaft simulating the focal pointof said driving ellipse and having rigid connection means with a firstconnecting means located at the point in space that is equivalent to theother focal point on the major axis of said driving ellipse, and asecond shaft simulating the opposite focal point of said driven ellipseand having second rigid connection means with a second connecting meanslocated at the point in space that is equivalent to the other focalpoint on the major axis of said driven ellipse; said first connectingmeans and said second connecting means being maintained in fixed spacedrelationship but free to move in a plane, and as opposite focal pointsby a connecting bar; and meshing means attached to said rigid connectionmeans and located at the points in space equivalent to the maximumdimensions of the major axis of each respective ellipse to move saidrigid connection means from dead center position and maintain saidshafts as opposite focal points.

25, The steering system of claim 24 wherein the distance between focalpoints of each respective ellipse and hence the distance between saidrespective shafts and connecting means is the major axis multipliedbythe cosine of an angle a generated by lines extended from a midpointbetween outside nonsteering wheels attached to said frame to one of thenonsteering wheels and to the steerable wheel on the same side as saidone of said nonsteering wheels, and the minor axis length is the majoraxis length multiplied by the sine of the angle a.

26. The steering system of claim 24 wherein the effective radius of saidrespective meshing means is equal to the ellipse major axis multipliedby(sinea)? 27. The steering system of claim 20 wherein said wheel steeringmeans is an electric motor turning an arrangement of gears connected soas to impart steer to said wheel in response to rotation of said motor.

28. The steering system of claim 20 wherein said actuator consistsessentially of a turn switch mounted on an operator's console andadapted for generating a turn left signal when moved in one directionand for generating a turn right signal when moved in another direction;a reversible electric motor electrically connected with said turn switchand operable to rotate in either direction in response to the particularturn signal from said turn switch.

29. The steering system of claim 20 wherein said selector means consistsessentially of a drive gear and meshing therewith an idler gear; saiddrive gear connected with a reversible electric motor of said actuatormeans and rotatably responsive to torque therefrom and operable toimpart torque to one controller means during turn in one direction,initiated from a position of of steer; and said idler gear maintained inengagement with said drive gear and rotatable about a fixed axis, andoperable to transmit torque from said drive gear to the other controllermeans during a turn in the opposite direction, initiated from 0 ofsteer.

30. Apparatus for steering a vehicle comprising:

a. a vehicle frame;

b. two wheels attached to said frame and separately steerable;

c. two wheel steering means, each connected, respectively, with one ofsaid wheels and operable to steer said wheel in response to a steersignal;

d. means for generating and imparting to a first one of the steeringmeans a first steer signal;

e. means for generating and imparting to a second of the steering meansa second steer signal; and

f. programmer means for establishing a relationship between said firstand second steer signals such that said second steer signal is relatedto said first steer signal as the degrees of rotation of a first focalpoint of a driven ellipse is related to the number of degrees ofrotation of the opposite first focal point of a driving ellipse rotatingtwice the number of degrees that the first wheel is steered in responseto the first steering signal; said ellipses being identical, beingplaced tangential such that their focal points on their major axes formthe apices of a rectangle at the position equivalent to 0 of steer,having a set of first and opposite focal points disposed a fixeddistance apart and located at points fixed in space, and having theirother, respective, and opposite focal points on their major axes infixed space relationship but free to move in a plane.

31. The steering system of claim 30 wherein said programmer meanscomprises identical ellipses having the relationships recited in element(f) and mounted on respective shafts located at said first and oppositefocal points for rotation about their first focal points and connectedtogether via connecting means located on said ellipses at theirrespective other and opposite focal points on their major axes; andwherein the distance between focal points on each respective ellipse andhence the distance between respective shafts and connecting means is themajor axis multiplied by the cosine of an angle a generated by linesextended from a midpoint between outside nonsteering wheels attached tosaid frame to one of the nonsteering wheels and to the steerable wheelon the same side as said one of said nonsteering wheels, and the minoraxis length of said ellipses is the major axis length multiplied by thesine of the angle a.

32. The steering system of claim 30 wherein said programmer meanscomprises as said ellipses a first shaft located at the first focalpoint of said driving ellipse and having rigid connection means with afirst connecting means located at the other focal point on the majoraxis of said driving ellipse, and a second shaft located at the oppositefirst focal point of said driven ellipse and having a second rigidconnection means with a second connecting means located at the otherfocal point on the major axis of said driven ellipse; said firstconnecting means and said second connecting means being maintained infixed spaced relationship but free to move in a plane, and as oppositefocal points by a connecting bar; and meshing means attached to saidrigid connection means and located at the points in space equivalent tothe maximum dimensions of the major axis of each respective ellipse tomove said rigid connection means from dead center position and maintainsaid shafts as opposite focal points.

33. The steering system of claim 32 wherein the distance between eachrespective shaft and connecting means along the respective rigidconnection means is the major axis of an equivalent ellipse multipliedby the cosine of an angle a generated by lines extended from a midpointbetween outside nonsteering wheels attached to said frame to one of thenonsteering wheels and to the steerable wheel on the same side as saidone of said nonsteering wheels, and said shafts and said connectingmeans are so spaced as to define a minor axis length of an equivalentellipse that is the major axis length multiplied by the sine of theangle a.

1. A method of steering a vehicle having two separately steerable wheelseach having a sensing-comparator, consisting essentially of the stepsof: a. generating a turn signal to effect a turn of the vehicle; b.selecting one of said wheels and the sensing-comparator associatedtherewith to be a primary wheel and a primary sensing-comparator forsaid turn; c. generating and imparting to said primarysensing-comparator a primary control signal which is a function of saidturn signal; d. sensing said primary control signal and in responsethereto generating and imparting to the other of said sensingcomparatorsa follower response signal which is related to said primary controlsignal as the number of degrees of rotation of a first focal point of adriven ellipse is related to a number of degrees of rotation of theopposite first focal point of a driving ellipse rotating twice thenumber of degrees that the primary steerable wheel is steered; saidellipses being identical, being placed tangential such that their focalpoints on their major axes form the apices of a rectangle at theposition equivalent to 0* of steer, having a set of first and oppositefocal points disposed a fixed distance apart and located at points fixedin space, and having their other, respective, and opposite focal pointson their major axes in fixed spaced relationship but free to move in aplane; e. steering said primary wheel through a number of degrees thatis a second function of said primary control signal; and f. steering theother wheel through a number of degrees that is said second function ofsaid follower response signal. CM,2Method of claim 1 wherein two outsidenonsteering wheels are also attached to said frame and said identicalellipses have a distance between the two focal points on each respectivemajor axis of each Ellipse that is equal to said major axis multipliedby the cosine of an angle Alpha generated by lines extending from amidpoint between said outside, nonsteering wheels attached to said frameto one of said outside, nonsteering wheels and to the steerable wheel onthe same side as said one of said outside, nonsteering wheels and saidellipses have each respective minor axis length that is equal to saidmajor axis length multiplied by the sine of the angle Alpha .
 3. Themethod of claim 2 wherein said primary wheel is the outside wheel on aturn and the driving ellipse rotates through a lesser number of degreesthan said driven ellipse.
 4. The method of claim 2 wherein said primarywheel is the inside wheel on a turn and said driving ellipse rotatesthrough a greater number of degrees than said driven ellipse.
 5. Themethod of claim 2 wherein said primary wheel is maintained as theprimary steerable wheel through steer in the opposite direction of saidturn until 0* of steer is again effected.
 6. The method of claim 2wherein a normal rate at which an inside wheel on a turn is steered isincreased to a higher rate at an angle between about one-fourth Beta andthree-fourths Beta , where Beta is the maximum angle the inside wheelwould be required to be steered to effect a turn of said vehicle aboutthe midpoint of a line connecting its nonsteering wheels.
 7. The methodof claim 6 wherein said higher rate is four times as great as saidnormal rate.
 8. The method of claim 1 wherein said primary wheel is theoutside wheel on a turn and the driving ellipse rotates through a lessernumber of degrees than said driven ellipse.
 9. The method of claim 1wherein said primary wheel is the inside wheel on a turn and saiddriving ellipse rotates through a greater number of degrees than saiddriven ellipse.
 10. The method of claim 1 wherein said primary wheel ismaintained as the primary steerable wheel through steer in the oppositedirection of said turn until 0* of steer is again effected.
 11. Themethod of claim 1 wherein a normal rate at which an inside wheel on aturn is steered is increased to a higher rate at an angle between aboutone-fourth Beta and three-fourths Beta , where Beta is the maximum anglethe inside wheel would be required to be steered to effect a turn ofsaid vehicle about the midpoint of a line connecting its nonsteeringwheels.
 12. The method of claim 11 wherein said higher rate is fourtimes as great as said normal rate.
 13. In a wheeled vehicle, a steeringsystem comprising: a. a vehicle frame; b. two wheels attached to saidframe and separately steerable, either of which may be a primarysteerable wheel or a secondary steerable wheel; c. two wheel steeringmeans, each connected, respectively, with one of said wheels andoperable to steer said wheel within a portion of a circle in response toa steer signal; d. two sensing-comparators, each connected,respectively, with one of said wheels and with the one of said wheelsteering means associated therewith and operable to generate a steersignal in response to a primary control signal or a follower responsesignal and operable to discontinue said steer signal when said wheel hasbeen steered through the number of degrees that is functionallyequivalent to, respectively, said primary control signal or saidfollower response signal; e. actuator means for actuating a turn bygenerating a turn signal; f. selector means connected with said actuatormeans and operable, in response to said turn signal, to select one ofsaid wheels as a primary steerable wheel for said turn and to impart toa controller means said turn signal; g. controller means connected withsaid selector means and operable to impart to the sensing-comparatormeans associated with said primary steerable wheel and to aprogrammer-follower a primary control signal that is a function of saidturn signal; h. a programmer-follower connected with said contRollermeans and operable to generate and impart to the sensing-comparatormeans associated with the secondary steerable wheel a follower responsesignal related to said primary control signal as the degrees of rotationof a first focal point of a driven ellipse is related to the number ofdegrees of rotation of the opposite first focal point of driving ellipserotating twice the number of degrees that said primary steerable wheelis steered; said ellipses being identical, being placed tangential suchthat their focal points on their major axes form the apices of arectangle at the position equivalent to 0* of steer, having a set offirst and opposite focal points disposed a fixed distance apart andlocated at points fixed in space, and having their other, respective,and opposite focal points on their major axes in fixed spacedrelationship but free to move in a plane.
 14. The steering system ofclaim 13 wherein said programmer employs as the equivalent of saidellipses a first shaft simulating the focal point of said drivingellipse and having rigid connection means with a first connecting meanslocated at the point in space that is equivalent to the other focalpoint on the major axis of said driving ellipse, and a second shaftsimulating the opposite focal point of said driven ellipse and havingsecond rigid connection means with a second connecting means located atthe point in space that is equivalent to the other focal point on themajor axis of said driven ellipse; said first connecting means and saidsecond connecting means being maintained in fixed spaced relationshipbut free to move in a plane, and as opposite focal points by aconnecting bar; and meshing means attached to said rigid connectionmeans and located at the points in space equivalent to the maximumdimensions of the major axis of each respective ellipse to move saidrigid connection means from dead center position and maintain saidshafts as opposite focal points.
 15. The steering system of claim 14wherein the distance between focal points of each respective ellipse andhence the distance between said respective shafts and connecting meansis the major axis multiplied by the cosine of an angle Alpha generatedby lines extended from a midpoint between outside nonsteering wheelsattached to said frame to one of the nonsteering wheels and to thesteerable wheel on the same side as said one of said nonsteering wheels,and the minor axis length is the major axis length multiplied by thesine of the angle Alpha .
 16. The steering system of claim 14 whereinthe effective radius of said respective meshing means is equal to theellipse major axis multiplied by (sine Alpha )2.
 17. The steering systemof claim 13 wherein said wheel steering means is an electric motorturning an arrangement of gears connected so as to impart steer to saidwheel in response to rotation of said motor.
 18. The steering system ofclaim 13 wherein said actuator consists essentially of a turn switchmounted on an operator''s console and adapted for generating a turn leftsignal when moved in one direction and for generating a turn rightsignal when moved in another direction; a reversible electric motorelectrically connected with said turn switch and operable to rotate ineither direction in response to the particular turn signal from saidturn switch.
 19. The steering system of claim 13 wherein said selectormeans consists essentially of a drive gear and meshing therewith anidler gear; said drive gear connected with said reversible electricmotor of said actuator means and rotatably responsive to torquetherefrom and operable to impart torque to one controller means duringturn in one direction, initiated from a position of 0* of steer; andsaid idler gear maintained in engagement with said drive gear androtatable about a fixed axis, and operable to transmit torque from saiddrive gear to the other controller means during a turn in the oppositedirection, initiated from 0* of steer.
 20. In a wheeled vehicle, asteering system comprising: a. a vehicle frame; b. two wheels attachedto said frame and separately steerable, either of which may be a primarysteerable wheel or a secondary steerable wheel; c. two wheel steeringmeans, each connected, respectively, with one of said wheels andoperable to steer said wheel within a portion of a circle in response toa steer signal; d. two position sensing means, each connected,respectively, with one of said wheels for sensing the number of degreesof steer of said wheel and for generating and transmitting a signal thatis a function of said degrees of steer; e. two comparator means, eachconnected, respectively, with one of said steering means and connectedwith the one of said position sensing means associated with one of saidsteering means, and operable to generate a steer signal in response to aprimary control signal or a follower response signal and to terminatesaid steer signal when said sensing means indicates said wheel has beensteered through the number of degrees that is functionally equivalentto, respectively, said primary control signal or said follower responsesignal; f. two controller means, each connected, respectively, with oneof said comparator means and operable to generate a primary controlsignal in response to a turn signal from an actuator or a followerresponse signal in response to a programmer; g. selector means connectedwith said two controller means and operable to impart a turn signalsingly and respectively to said controller means; h. actuator meansconnected with said selector means for generating a turn signal foractuating a turn; i. a programmer connected with said two controllermeans and operable to receive a primary control signal from either ofsaid controller means and in response thereto, to generate and transmitto the other of said controller means a follower response signal, saidprogrammer having signal translating means effecting a ratio of saidfollower response signal to said primary control signal that is the sameas the ratio of the degrees of rotation of a first focal point of adriven ellipse to the number of degrees of rotation of the oppositefirst focal point of a driving ellipse rotating twice the number ofdegrees that said primary steerable wheel is steered; said ellipsesbeing identical, being placed tangential such that their focal points ontheir major axes form the apices of a rectangle at the positionequivalent to 0* of steer, having a set of first and opposite focalpoints disposed a fixed distance apart and located at points fixed inspace, and having their other, respective, and opposite focal points ontheir major axes in fixed spaced relationship but free to move in aplane.
 21. The steering system of claim 20 wherein said position sensingmeans consists essentially of a position sensor sensing the degrees ofsteer of the respective wheel with which it is associated and generatinga unique signal which is a function of said degrees of steer, a selsyntransmitter generating and transmitting a signal unique to the positionindicated by said position sensor, a slave selsyn receiver connectedwith said selsyn transmitter and adapted to assume a slave position foreach unique signal therefrom, said slave position being relatable to thedegrees of steer of said wheel, and a slave pivotable indicator plateresponsively connected with said slave selsyn receiver and adapted toassume said slave position.
 22. The steering system of claim 20 whereinsaid comparator means consists essentially of a holder having at each ofits two U-shaped ends a light source and an electronic device renderedconductive by said light source, each electronic device being connectedin a circuit with a power source and one of said wheel steering meansand operable to send a directional steer signal to said one of saidwheel steering means when bombarded by light from said light source. 23.The steering system of claim 20 wherein said controller means is asector gear rotatable about a fixed axis in response, respectively, tourging from said selector means or said programmer.
 24. The steeringsystem of claim 20 wherein said programmer employs as the equivalent ofsaid ellipses a first shaft simulating the focal point of said drivingellipse and having rigid connection means with a first connecting meanslocated at the point in space that is equivalent to the other focalpoint on the major axis of said driving ellipse, and a second shaftsimulating the opposite focal point of said driven ellipse and havingsecond rigid connection means with a second connecting means located atthe point in space that is equivalent to the other focal point on themajor axis of said driven ellipse; said first connecting means and saidsecond connecting means being maintained in fixed spaced relationshipbut free to move in a plane, and as opposite focal points by aconnecting bar; and meshing means attached to said rigid connectionmeans and located at the points in space equivalent to the maximumdimensions of the major axis of each respective ellipse to move saidrigid connection means from dead center position and maintain saidshafts as opposite focal points. 25, The steering system of claim 24wherein the distance between focal points of each respective ellipse andhence the distance between said respective shafts and connecting meansis the major axis multiplied by the cosine of an angle Alpha generatedby lines extended from a midpoint between outside nonsteering wheelsattached to said frame to one of the nonsteering wheels and to thesteerable wheel on the same side as said one of said nonsteering wheels,and the minor axis length is the major axis length multiplied by thesine of the angle Alpha .
 26. The steering system of claim 24 whereinthe effective radius of said respective meshing means is equal to theellipse major axis multiplied by (sine Alpha )2.
 27. The steering systemof claim 20 wherein said wheel steering means is an electric motorturning an arrangement of gears connected so as to impart steer to saidwheel in response to rotation of said motor.
 28. The steering system ofclaim 20 wherein said actuator consists essentially of a turn switchmounted on an operator''s console and adapted for generating a turn leftsignal when moved in one direction and for generating a turn rightsignal when moved in another direction; a reversible electric motorelectrically connected with said turn switch and operable to rotate ineither direction in response to the particular turn signal from saidturn switch.
 29. The steering system of claim 20 wherein said selectormeans consists essentially of a drive gear and meshing therewith anidler gear; said drive gear connected with a reversible electric motorof said actuator means and rotatably responsive to torque therefrom andoperable to impart torque to one controller means during turn in onedirection, initiated from a position of 0* of steer; and said idler gearmaintained in engagement with said drive gear and rotatable about afixed axis, and operable to transmit torque from said drive gear to theother controller means during a turn in the opposite direction,initiated from 0* of steer.
 30. Apparatus for steering a vehiclecomprising: a. a vehicle frame; b. two wheels attached to said frame andseparately steerable; c. two wheel steering means, each connected,respectively, with one of said wheels and operable to steer said wheelin response to a steer signal; d. means for generating and imparting toa first one of the steering means a first steer signal; e. means forgenerating and imparting to a second of the steering means a secondsteer signal; and f. programmer means for establishing a relationshipbetween said first and second steer signals such that said second steersignal is related to said first steer signal as the degrees of rotatiOnof a first focal point of a driven ellipse is related to the number ofdegrees of rotation of the opposite first focal point of a drivingellipse rotating twice the number of degrees that the first wheel issteered in response to the first steering signal; said ellipses beingidentical, being placed tangential such that their focal points on theirmajor axes form the apices of a rectangle at the position equivalent to0* of steer, having a set of first and opposite focal points disposed afixed distance apart and located at points fixed in space, and havingtheir other, respective, and opposite focal points on their major axesin fixed space relationship but free to move in a plane.
 31. Thesteering system of claim 30 wherein said programmer means comprisesidentical ellipses having the relationships recited in element (f) andmounted on respective shafts located at said first and opposite focalpoints for rotation about their first focal points and connectedtogether via connecting means located on said ellipses at theirrespective other and opposite focal points on their major axes; andwherein the distance between focal points on each respective ellipse andhence the distance between respective shafts and connecting means is themajor axis multiplied by the cosine of an angle Alpha generated by linesextended from a midpoint between outside nonsteering wheels attached tosaid frame to one of the nonsteering wheels and to the steerable wheelon the same side as said one of said nonsteering wheels, and the minoraxis length of said ellipses is the major axis length multiplied by thesine of the angle Alpha .
 32. The steering system of claim 30 whereinsaid programmer means comprises as said ellipses a first shaft locatedat the first focal point of said driving ellipse and having rigidconnection means with a first connecting means located at the otherfocal point on the major axis of said driving ellipse, and a secondshaft located at the opposite first focal point of said driven ellipseand having a second rigid connection means with a second connectingmeans located at the other focal point on the major axis of said drivenellipse; said first connecting means and said second connecting meansbeing maintained in fixed spaced relationship but free to move in aplane, and as opposite focal points by a connecting bar; and meshingmeans attached to said rigid connection means and located at the pointsin space equivalent to the maximum dimensions of the major axis of eachrespective ellipse to move said rigid connection means from dead centerposition and maintain said shafts as opposite focal points.
 33. Thesteering system of claim 32 wherein the distance between each respectiveshaft and connecting means along the respective rigid connection meansis the major axis of an equivalent ellipse multiplied by the cosine ofan angle Alpha generated by lines extended from a midpoint betweenoutside nonsteering wheels attached to said frame to one of thenonsteering wheels and to the steerable wheel on the same side as saidone of said nonsteering wheels, and said shafts and said connectingmeans are so spaced as to define a minor axis length of an equivalentellipse that is the major axis length multiplied by the sine of theangle Alpha .